One simple example (which I'm probably mixing up) is "making tens"; when doing addition or subtraction, rather than blindly memorizing a bunch of facts like "3+8=11", they learn to break the numbers up, so you take 3 and 8, "make a ten", and have one left over.
This is actually a great thing to help with understanding of what's going on with math, and after my kids showed me a few examples, I totally got it. But for those who are less open to new ways of teaching, it may just seem like change for the sake of change. And it's not just math; they're also teaching other subjects (such as writing) in newer ways, which I honestly think are fantastic - having kids spend time writing every day is great.
There are also quite a few bad questions in the workbooks; this has probably always been true, but the combination of bad question plus unfamiliar (to parents) concepts causes a strong reaction. Plus the whole "the gubmint is trying to brainwash mah kids!" contingent overreacting about everything....
My, I'd be happy if we had military dictatorship which imposed a new order including the metric system, radians instead of degrees and algebra from 1st grade onward. But I don't think that program would have a sufficient constituency.